In a conventional digital-to-analog conversion. there has been a method wherein after converting a digital signal sampled in synchronism with a sampling pulse into a pulse width signal having a pulse width corresponding to the digital value of the digital signal, the pulse width signal is decoded through a filter circuit into an analog signal. In such a prior art, in case that the digital signal is converted into the pulse width signal, as shown in FIG. 1, since the pulse widths T.sub.1, T.sub.2, T.sub.3 - - - of the pulse width signals S.sub.0 are determined by time period from sampling times t.sub.1, t.sub.2, t.sub.3 - - - corresponding to the sampling pulse of the sampling signal P.sub.0, the center of each pulse width of the pulse width signals S.sub.0 tends to vary in accordance with the digital value of the sampled digital signal.
Accordingly, as shown in FIG. 2B, in the waveform S'.sub.A of the analog signal decoded by filtering the pulse width signal, the period T'a between the top and bottom of the waveform S'.sub.A, during which the level of the analog signal decreases, is compressed relative to the corresponding period Ta of the waveform S.sub.A of the original analog signal as shown in FIG. 2A, while the period T'b between the bottom and top of the waveform S'.sub.A, during which the level of the analog signal increases, is expanded relative to the corresponding period Tb of the original waveform S.sub.A. Thus, it will be noted that the decoded analog signal is distorted. Such a distortion of the analog signal is negligible in case that the frequency of the sampling signal is fully higher than that of the analog signal, but it is disadvantageously considerable in case that the former frequency is a few times as many as the latter frequency.